Toughen callable usage.

Not all callable types can be invoked using $foo(...). Use
call_user_func() as it correctly handles all callable types.

Change _bindParams to _bindStatement as it takes a statement and binds
the query into the statement.
Implement UUID type.

UUID's are just simple strings as far as PDO drivers would be concerned.
Add start of decimal type.

Since PDO doesn't have special float bindings, we'll treat decimals as
strings. Since PHP doesn't have special decimal types, we'll treat them
as floats.